Semiconductor device structures including vertical transistor devices, arrays of vertical transistor devices, and methods of fabrication

ABSTRACT

A semiconductor device structure is disclosed. The semiconductor device structure includes a mesa extending above a substrate. The mesa has a channel region between a first side and second side of the mesa. A first gate is on a first side of the mesa, the first gate comprising a first gate insulator and a first gate conductor comprising graphene overlying the first gate insulator. The gate conductor may comprise graphene in one or more monolayers. Also disclosed are a method for fabricating the semiconductor device structure; an array of vertical transistor devices, including semiconductor devices having the structure disclosed; and a method for fabricating the array of vertical transistor devices.

TECHNICAL FIELD

The invention, in various embodiments, relates generally to the field ofintegrated circuit design and fabrication. More particularly, thisdisclosure relates to vertically-oriented transistors and methods forfabricating the transistors.

BACKGROUND

Fabricating a semiconductor device, such as a transistor, upon asubstrate necessarily leads to occupation of a certain surface area ofthe substrate by the footprint of the device. Often, the availablesurface area of a given substrate is limited, and maximizing the use ofthe substrate requires maximizing the density of devices fabricated onthe substrate. Minimizing the dimensions of components of a device, suchas a transistor, accommodates minimizing the overall footprint of thedevice and maximizing of the device density. This accommodates formationof a greater number of devices on a given substrate.

Transistors are often constructed upon the primary surface of thesubstrate. The primary surface is generally the upper-most, exteriorsurface of the substrate. The primary surface of the substrate isconsidered to define a horizontal plane and direction.

Field effect transistor (“FET”) structures, which include a channelregion between a pair of source/drain regions and a gate configured toelectrically connect the source/drain regions to one another through thechannel region, can be divided amongst two broad categories based on theorientations of the channel regions relative to the primary surface ofthe substrate. Transistor structures that have channel regions that areprimarily parallel to the primary surface of the substrate are referredto as planar FET structures, and those having channel regions that aregenerally perpendicular to the primary surface of the substrate arereferred to as vertical FET (“VFET”) transistor structures. Becausecurrent flow between the source and drain regions of a transistor deviceoccurs through the channel region, planar FET devices can bedistinguished from VFET devices based upon both the direction of currentflow as well as on the general orientation of the channel region. VFETdevices are devices in which the current flow between the source anddrain regions of the device is primarily substantially orthogonal to theprimary surface of the substrate. Planar FET devices are devices inwhich the current flow between source and drain regions is primarilyparallel to the primary surface of the substrate.

A VFET device includes a vertical, so-called “mesa,” also referred to inthe art as a so-called “fin,” that extends upward from the underlyingsubstrate. This mesa forms part of the transistor body. Generally, asource region and a drain region are located at the ends of the mesawhile one or more gates are located on one or more surfaces of the mesaor fin. Upon activation, current flows through the channel region withinthe mesa.

VFETs are generally thinner in width (i.e., in the dimension in a planeparallel to the horizontal plane defined by the primary surface of thesubstrate) than planar FETs. Therefore, vertical transistors areconducive to accommodating increased device packing density and areconducive for inclusion within a cross-point memory array. In such anarray, multiple VFETs are ordered in stacked rows and columns. However,even with this arrangement, the packing density is at least partiallylimited by the minimal dimensions of the components of the verticaltransistor, including the gate and channel components.

Scaling or otherwise reducing the dimensions of transistor componentsdepends, at least in part, on the limitations of conventionalsemiconductor fabrication techniques, physical limitations of materialsused in the fabrication, and minimal properties required for fabricatingan operational device. For example, to form a typical gate metal havingthe properties to achieve the necessary level of low electricalresistance, a gate thickness of greater than 5 nanometers is generallyrequired. Using a gate metal of 5 nm thickness in a VFET device having asurround gate, the total width of the device must take into accounttwice the width of the gate material. Therefore, a typical VFET surroundgate will have at least 10 nanometers of the VFET device's widthconsumed by the gate conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional, top and front perspective, schematic viewof a vertical field effect transistor of an embodiment of the presentdisclosure;

FIGS. 2-11 are cross-sectional, top and front perspective, schematicviews of a semiconductor device structure during various stages ofprocessing according to an embodiment of the present disclosure; and

FIGS. 12-21 are cross-sectional, top and front perspective, schematicviews of a semiconductor device structure during various stages ofprocessing according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

A semiconductor device structure, an array of vertical transistordevices, and methods for fabricating such structures or devices aredisclosed. The vertical transistor device and array of VFETs all includethin gate conductors, making the present VFET structure and methodconducive in high-device-density integrated circuit designs, includingcross-point memory arrays.

As used herein, the term “substrate” means and includes a base materialor construction upon which materials, such as vertical field effecttransistors, are formed. The substrate may be a semiconductor substrate,a base semiconductor layer on a supporting structure, a metal electrodeor a semiconductor substrate having one or more layers, structures orregions formed thereon. The substrate may be a conventional siliconsubstrate or other bulk substrate comprising a layer of semiconductivematerial. As used herein, the term “bulk substrate” means and includesnot only silicon wafers, but also silicon-on-insulator (“SOI”)substrates, such as silicon-on-sapphire (“SOS”) substrates orsilicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on abase semiconductor foundation or other semiconductor or optoelectronicmaterials, such as silicon-germanium (Si_(1-x)Ge_(x)), germanium (Ge),gallium arsenide (GaAs), gallium nitride (GaN), or indium phosphide(InP). Furthermore, when reference is made to a “wafer” or “substrate”in the following description, previous process steps may have beenutilized to form regions or junctions in the base semiconductorstructure or foundation.

As used herein, the term “graphene” means and includes a poly-cyclicaromatic molecule having a plurality of carbon atoms that are connectedto each other by covalent bonds. The plurality of carbon atoms may forma plurality of six-member rings, which function as a standard repeatingunit, and may further include a five-membered ring and/or aseven-membered ring. The graphene may be a one atom thick material ofthe six-member rings in which the carbon atoms are covalently bonded andhave sp² hybridization. The graphene may include the monolayer ofgraphene. Alternatively, the graphene may include multiple monolayers ofgraphene stacked upon one another. In this regard, the graphene may havea maximum thickness of about 5 nanometers. If multiple monolayers ofgraphene are used, the graphene may be used as a gate in a semiconductordevice structure. If a one atom thick material is used, the graphene maybe used as a switchable material.

As used herein, while the terms “first,” “second,” “third,” etc., maydescribe various elements, components, regions, layers, and/or sections,none of which are limited by these terms. These terms are used only todistinguish one element, component, region, material, layer, or sectionfrom another element, component, region, material, layer, or section.Thus, “a first element,” “a first component,” “a first region,” “a firstmaterial,” “a first layer,” or “a first section” discussed below couldbe termed a second element, a second component, a second region, asecond material, a second layer, or second section without departingfrom the teachings herein.

As used herein, spatially relative terms, such as “beneath,” “below,”“lower,” “bottom,” “above,” “upper,” “top,” “front,” “rear,” “left,”“right,” and the like, may be used for ease of description to describeone element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. Unless otherwise specified,the spatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if a device in thefigures is turned over, elements described as “below” or “beneath” or“under” or “on bottom of other elements or features would then beoriented “above” or “on top of the other elements or features. Thus, theterm “below” can encompass both an orientation of above and below,depending on the context in which the tern is used, which will beevident to one of ordinary skill in the art. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

As used herein, reference to an element as being “on” another elementmeans and includes the element being directly on top of, adjacent to,underneath, or in direct contact with the other element. It alsoincludes the element being indirectly on top of, adjacent to,underneath, or near the other element, with other elements presenttherebetween. In contrast, when an element is referred to as being“directly on” another element, there are no intervening elementspresent.

As used herein, the terms “comprises,” “comprising,” “includes,” and/or“including” specify the presence of stated features, regions, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, regions, integers,steps, operations, elements, components, and/or groups thereof.

As used herein, “and/or” includes any and all combinations of one ormore of the associated listed items.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

The illustrations presented herein are not meant to be actual views ofany particular component, structure, device, or system, but are merelyidealized representations that are employed to describe embodiments ofthe present disclosure.

Example embodiments are described herein with reference to crosssectional illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes or regions as illustratedbut are to include deviations in shapes that result, for example, frommanufacturing. For example, a region illustrated or described as boxshape may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

The following description provides specific details, such as materialtypes, material thicknesses, and processing conditions in order toprovide a thorough description of embodiments of the disclosed devicesand methods. However, a person of ordinary skill in the art willunderstand that the embodiments of the devices and methods may bepracticed without employing these specific details. Indeed, theembodiments of the devices and methods may be practiced in conjunctionwith conventional semiconductor fabrication techniques employed in theindustry.

The fabrication processes described herein do not form a completeprocess flow for processing semiconductor device structures. Theremainder of the process flow is known to those of ordinary skill in theart. Accordingly, only the methods and semiconductor device structuresnecessary to understand embodiments of the present devices and methodsare described herein.

Unless the context indicates otherwise, the materials described hereinmay be formed by any suitable technique including, but not limited to,spin coating, blanket coating, chemical vapor deposition (“CVD”), atomiclayer deposition (“ALD”), plasma enhanced ALD, and physical vapordeposition (“PVD”). Alternatively, the materials may be grown in situ.Depending on the specific material to be formed, the technique fordepositing or growing the material may be selected by a person ofordinary skill in the art.

Unless the context indicates otherwise, the removal of materialsdescribed herein may be accomplished by any suitable techniqueincluding, but not limited to, etching, abrasive planarization, or otherknown material-removal methods.

Reference will now be made to the drawings, where like numerals refer tolike components throughout. The drawings are not necessarily drawn toscale.

FIG. 1 is a cross-sectional, front and top perspective view of aschematic of a VFET 100 semiconductor device having a structure of thepresent disclosure. The VFET 100 includes a mesa 120 extending above asubstrate 50 such that a bottom side 125 of the mesa 120 sits on ahorizontally planar upper surface of the substrate 50. The mesa 120extends above the substrate 50 in a direction perpendicular to thesubstrate 50. The mesa 120 has a first side 121 and a second side 122that is opposite and substantially parallel to the first side 121. Achannel region 130 passes through the mesa 120 between the first side121 and the second side 122. In use and operation, the channel region130 is configured to allow current to flow between a source region (notshown) and a drain region (not shown). A top side 126 of the mesa 120may be in operable communication with an electrode (not shown) orinterconnect (not shown).

A first gate 140 is provided on the first side 121 of the mesa 120. Thefirst gate 140 is operative to control current flow in the channelregion 130. A second gate 140 may be provided on the second side 122 ofthe mesa 120, as well, the second gate 140 being operative to control,in conjunction with the first gate 140, current flow in the channelregion 130 of the mesa 120.

Each gate 140 includes a gate insulator 160 and an overlying gateconductor 150. The gate insulator 160 may be provided directly on thefirst and/or second sides 121, 122 of the mesa 120. The gate conductor150 may be provided directly on the gate insulator 160 and may surroundthe vertical sides of the mesa 120, i.e., may surround the first side121, the second side 122, a third side 123, and a fourth side 124 of themesa 120. In such embodiments, the third side 123 and fourth side 124may be opposite and parallel one another and arranged perpendicularly tothe first side 121 and the second side 122.

In other embodiments of the present VFET 100 structure, the gate 140 isprovided only on the first side 121 of the mesa 120. In still otherembodiments, the gate 140 is provided only on the first side 121 andsecond side 122 of the mesa 120, but not on the third side 123 or thefourth side 124.

According to the embodiment of the present VFET 100 structure depictedin FIG. 1, the gate conductor 150 of the sidewall gate structure 140substantially overlies the entire exterior surface of the gate insulator160 (i.e., the surface of the gate insulator 160 that is opposite andsubstantially parallel to the surface of the gate insulator 160 that isproximate to the mesa 120). In other embodiments of the VFET 100structure, the gate conductor 150 of the gate 140 overlies only aportion of the exterior surface of the gate insulator 160. In some suchembodiments, the gate conductor 150 is structured as a ring-gateconductor.

The gate conductor 150 of the present VFET 100 is a gate conductor,defining a gate conductor thickness G (i.e., the dimension of theshortest side of the gate conductor 150, when such gate conductor 150 isconstrued as having a three-dimensional box shape) of less than or equalto about 5 nanometers. Therefore, according to the depicted VFET 100having a pair of gates 140, the thickness of the gate conductor 150contributes twice the thickness G of the gate conductor 150 to theoverall width C of one formed VFET cell (FIG. 11 and FIG. 21). Thethickness G of the gate conductor 150 may be less than the thickness Iof the gate insulator 160, which is defined by the dimension of theshortest side of the gate insulator 160, when such gate insulator 160 isconstrued as having a three-dimensional box shape.

The gate conductor 150 may be formed from graphene, or at least aportion of the gate conductor 150 may include graphene. Grapheneexhibits high electrical conductivity and has a single atom bodythickness. Therefore, graphene possesses great potential for high-speedelectronics. Generally, graphene is a one-atom thick planar sheet ofsp²-bonded carbon atoms that are densely packed in a honeycomb latticesuch that the carbon atoms of graphene sheets are connected to eachother in an extended array of hexagonal rings. Individual graphenesheets may be stacked. Therefore, the gate conductor 150 may include aplurality of layers of graphene. If multiple monolayers of graphene areused, the graphene may be used as the gate conductor 150. If a one atomthick material is used, the graphene may be used as a switchablematerial in the semiconductor device.

A semiconductor device structure including the vertical transistordevices comprises a mesa extending above a substrate and a first gate onthe first side of the mesa is disclosed. The mesa comprises a channelregion between a first side and a second side of the mesa. The firstgate comprises a first gate insulator and a first gate conductorcomprising graphene overlying the first gate insulator.

FIGS. 2-11 depict various stages of processing of a plurality ofvertical transistors in accordance with embodiments of the presentmethod for fabricating a semiconductor device, such as a VFET 100device, as well as for fabricating an array 300 (FIG. 10) of verticaltransistor devices 100. With particular reference to FIG. 2, the presentmethod includes forming a plurality of metal seeds 110 upon a substrate50. The metal seeds 110 are spaced from one another and arranged inparallel. The metal seeds 110 may be formed at pitch. Each metal seed110 includes a first side 111, second side 112, bottom side 115, and topside 116. According to the depiction in FIG. 2, the metal seeds 110 arepositioned such that the bottom side 115 of each metal seed 110 isadjacent to the substrate 50, and the top side 116 of each metal seed110 is opposite the bottom side 115 and directed upward from substrate50. The first side 111 of one metal seed 110 is positioned opposite andparallel to the second side 112 of a neighboring metal seed 110. Themetal seeds 110 may be evenly spaced from one another, arranged inparallel, such that each metal seed 110 is separated from each adjacentand parallel metal seed 110 by a trench having a width M equal to afirst distance. In other embodiments, the metal seeds 110 may be spacedunevenly from one another such that one metal seed 110 is spaced furtherfrom a first neighboring metal seed 110 than it is spaced from a secondneighboring metal seed 110. In still other embodiments, the metal seeds110 may be spaced unevenly such that one metal seed 110 is spacedfurther from a neighboring metal seed 110 at a first end than it isspaced from the neighboring metal seed 110 at a second end.

The material of the metal seed 110 may be any metal conducive forforming a gate conductor 150, such as a gate conductor of graphene,thereupon. For example, without limitation, copper, nickel, iridium,ruthenium, combinations thereof, and solid mixtures containing any orall of these metals may be used as the material of the metal seed 110.As a more particular example, the metal seed 110 may be formed fromcopper, such as polycrystalline copper.

With reference to FIG. 3, the method for fabricating a semiconductordevice, such as a VFET device 100, or VFET array 300, further includesforming a conductor material upon each of the plurality of metal seeds110 to form a gate conductor 150, including gate conductor sidewallsaligning each of the first sides 111 and second sides 112 of the metalseeds 110. The conductor material may be formed conformally over thefirst side 111, second side 112, and top side 116 of the metal seeds110. The conductor material of the gate conductors 150 may be formed byany suitable technique, including, but not limited to, CVD, ALD,plasma-enhanced ALD, or other known methods. Portions of the conductormaterial overlying an upper surface of the substrate 50, if any, may beremoved by conventional techniques, exposing the substrate 50.

The conductor material of the gate conductor 150 may be formed ofgraphene. Various methods of forming graphene are known. U.S. Pat. No.7,071,258, which issued Jul. 4, 2006, to Jang et al.; U.S. Pat. No.7,015,142, which issued Mar. 21, 2006, to DeHeer et al.; U.S. Pat. No.6,869,581, which issued Mar. 22, 2005, to Kishi et al.; U.S. PatentApplication Publication No. 2011/0123776, which published May 26, 2011,for Shin et al.; and U.S. Patent Application Publication No.2006/0099750, which published May 11, 2006, for DeHeer et al. describevarious methods of forming graphene. Any such suitable technique may beused to form the gate conductor 150 from graphene on the metal seeds110. For example, without limitation, in some embodiments, graphene maybe formed using ALD, CVD, or other known methods.

In such embodiments, the graphene may be formed directly upon theexterior surface of the metal seeds 110. According to the depiction ofFIG. 3, the conductor material may overlay at least the first side 111,top side 116, and second side 112 of each metal seed 110 of theplurality of metal seeds 110, but may not overlay the upper surface ofthe substrate 50. Regardless of how formed, the gate conductor 150formed from graphene may have a thickness of only one atom.Alternatively, the gate conductor 150 formed from graphene may includebi-, tri-, or other multi-layer graphene.

In other embodiments of the disclosed method, the conductor material maybe formed so as to form the depicted gate conductor 150 sidewalls andtopwall and to overlay the upper surface of the substrate 50. Thesemiconductor device may be thereafter suitably processed to remove theconductor material overlying the substrate 50, such as usingphotolithography, etching, or other known methods, to produce, at least,gate conductor 150 sidewalls overlying the first side 111 and secondside 112 of each of the metal seeds 110, but not on the upper surface ofthe substrate 50 positioned between the metal seeds 110.

With reference to FIG. 4, the present method further includes forming aninsulator material upon each of the plurality of gate conductor 150sidewalls to form a plurality of gate insulator 160 sidewalls. Themethod may further include forming the insulator material upon a gateconductor 150 topwall or top side 116 of the metal seeds 110. The methodmay further include forming the insulator material upon a gate conductor150 bottomwall positioned between the metal seeds 110 or upon an exposedsubstrate 50 surface positioned between the metal seeds 110. Theinsulator material may be conformally formed over the gate conductor 150sidewalls and topwall and the remaining exposed substrate 50 surface.Thus, according to the depiction in FIG. 4, the insulator material isformed upon each of the gate conductor 150 sidewalls and topwall and theremaining exposed substrate 50 surface. Forming the insulator materialupon the gate conductor 150 sidewalls may include forming a seedmaterial directly upon the gate conductor 150 sidewalls before formingthe insulator material upon the gate conductor 150 sidewalls. As such,the formed gate insulator 160 sidewalls may include both the seedmaterial and the insulator material. As formed, a first gate insulator160 sidewall of the plurality of gate insulator 160 sidewalls isseparated from a second gate insulator 160 sidewall of the plurality bya first trench 170. Because the metal seeds 110 may be evenly spaced inparallel from one another, the formed gate insulator 160 sidewalls maybe evenly spaced from one another, such that each first trench 170defines a first trench width T. First trench width T is less than thefirst distance of width M (FIG. 2) separating the metal seeds 110. Thefirst trench width T is equal to the width M decreased by twice thethickness of the insulator material of the first gate insulator 160 andtwice the thickness of the conductor material of the first gateconductor 150.

The gate insulator 160 sidewalls, topwall, or bottomwall may be formedby any suitable technique, including, but not limited to, CVD, ALD,plasma-enhanced ALD, PVD, or other known methods. In one embodiment, thegate insulator 160 is formed by ALD. The insulator material of the gateinsulator 160 may be any suitable insulative material. For example,without limitation, the gate insulator 160 may be formed from an oxide.

With reference to FIG. 5, the present method may further include fillingthe first trenches 170 with a second insulator material 180. The secondinsulator material 180 may not only fill the first trenches 170, but mayalso cover the gate insulator 160 topwall. Filling the first trenches170 with the second insulator material 180 may be accomplished by anysuitable method, including, without limitation, by spin coating, blanketcoating, CVD, or other known methods. The second insulator material 180may be formed from any suitable insulative material. For example,without limitation, the second gate insulator 160 may be formed from aconventional interlayer dielectric (“ILD”) material, such as siliconoxide or silicon nitride.

In other embodiments of the disclosed method, filling the trenches 170with the second insulator material 180 may include filling only thetrenches 170 with the second insulator material 180, and not overlyingthe second insulator material 180 upon the top sides 116 of the metalseeds 110, the topwall of the gate conductor 150 material, or thetopwall of the gate insulator 160 material.

With reference to FIG. 6, the method may further include, if necessary,removing portions of the second insulator material 180, portions of thegate insulator 160 material, and portions of the gate conductor 150material, to expose the top sides 116 of the metal seeds 110. This maybe accomplished by any suitable method, including, without limitation,planarization methods such as abrasive planarization, chemicalmechanical polishing or planarization (“CMP”) or an etching process.

The method may further include removing the metal seeds 110 and fillingthe spaces once occupied by the metal seeds 110 with a material having amelting temperature greater than the metal temperature of the materialforming the metal seeds 110. As such, the re-filled material may beconfigured to withstand, without substantial deformation, higherfabrication temperatures than the metal seeds 110 could withstand.

With reference to FIGS. 7 through 9, the method may further includeselectively removing segments of the second insulator material 180 toexpose underlying sections of the substrate 50. The removed segments ofsecond insulator material 180 may be spaced segments. The removedsegments define a plurality of cavities 200 in the second insulatormaterial 180. The removal of the segments of second insulator material180 may be accomplished by patterning in a direction orthogonal to thesubstrate 50, such as by use of a photomask 190 that leaves exposed thetop surface of ordered segments of second insulator material 180.Etching or any other suitable method may be used to remove the segmentsof second insulator material 180 in accordance with the photomask 190pattern, as depicted in FIG. 8, after which, the photomask 190 may beremoved (FIG. 9).

According to the depicted method, each cavity 200 is formed in athree-dimensional box shape, such that a first side 201 is parallel andopposite to a second side 202 of the cavity, each of which is borderedand defined by a gate insulator 160 sidewall. A third side 203 andfourth side 204 of each cavity 200 are also parallel and opposite oneanother, being bordered and defined by remaining second insulatormaterial 180.

Where the method, in forming gate insulator 160 material results in gateinsulator 160 bottomwalls formed upon the substrate 50, a bottom side205 of each cavity 200 may be bordered and defined by gate insulator 160material, as shown in FIG. 8. In some embodiments, the gate insulator160 material may then be removed, as by etching or other knownmaterial-removal methods, and the gate insulator 160 material re-formedon the gate conductor 150 material. This intermediate process ofremoving and reforming the gate insulator 160 material may accommodateforming a gate insulator 160 material of optimal electrical quality inthe resulting array 300 of vertical transistor devices.

The photomask 190 may be further utilized to remove the sections of thegate insulator 160 material overlaying the substrate 50 so as to exposethose sections of the substrate 50 that were covered, as depicted inFIG. 9, before the photomask 190 is removed. Thereafter, the bottom side205 of each cavity 200 is bordered and defined by the exposed uppersurface of the substrate 50. The top side 206 of each cavity 200 remainsopen.

With reference to FIG. 10, the present method for forming asemiconductor device, such as a VFET device 100 or an array of VFETs300, further includes filling the cavities 200 with a channel material.The channel material forms mesas 120 bordered, as shown in FIG. 1, on afirst side 121 by a first gate insulator 160 sidewall, bordered on asecond side 122 by a second gate insulator 160 sidewall, and bordered ona third side 123 and fourth side 124 by remaining second insulatormaterial 180. The mesas 120 of a column of VFET devices may be spacedapart by second insulator material 180.

Filling the cavities 200 with the channel material to form the mesas 120may be accomplished with any suitable technique, including, withoutlimitation, spin coating, blanket coating, CVD, ALD, plasma-enhancedALD, PVD, in situ growth, or other known methods. The channel materialof the mesas 120 may be, without limitation, amorphous silicon,polycrystalline silicon, epitaxial-silicon, indium gallium zinc oxide(InGaZnOx) (“IGZO”), among others. In one embodiment, the channelmaterial is IGZO.

As depicted in FIG. 10, following the filling of the cavities 200 withthe channel material to form the mesas 120, each gate conductor 150sidewall remains bordered by a gate insulator 160 sidewall and one ofthe metal seeds 110. The semiconductor device structure of the presentdisclosure, therefore, may include a first metal seed 110 provided on afirst gate conductor 150 sidewall and a second metal seed 110 providedon the second gate conductor 150 sidewall.

As depicted in FIG. 11, the present method may further include removingthe metal seeds 110. Removing the metal seeds 110 may be accomplishedwith any suitable technique, such as etching. Removing the metal seeds110 produces second trenches 210 positioned between a pair ofoppositely-disposed gate conductor 150 sidewalls. Therefore, an array300 of VFETs 100 is formed, each VFET device 100 having at least onegate conductor 150.

A method for fabricating a semiconductor device structure is alsodisclosed. The method comprises forming a plurality of metal seedmaterials upon a substrate, forming a conductor material upon each ofthe plurality of metal seed materials to form a plurality of gateconductors, forming an insulator material upon each of the plurality ofgate conductors to form a plurality of gate insulators, and filling thefirst trench with a channel material to form a channel region. A firstgate insulator of the plurality of gate insulators is separated from asecond gate insulator of the plurality of gate insulators by a firsttrench.

With further regard to FIG. 11, the disclosed array 300 of verticaltransistor devices includes a first plurality of mesas 120 disposed onthe substrate 50. The first plurality of mesas 120 may include the mesas120 of a column of formed VFET devices 100. Each of the mesas 120 of thefirst plurality of mesas 120 has a first side 121 and a second side 122opposite the first side 121. The first sides 121 of the mesas 120 withinthe first plurality of mesas 120 are aligned with one another, and thesecond sides 122 of the mesas 120 within the first plurality are alignedwith one another.

The array 300 further includes a first plurality of segments ofinsulator material, such as segments of remaining second insulatormaterial 180, each of the segments of insulator material 180 separatingone of the mesas 120 from another mesa 120 within the first plurality ofmesas 120.

The array 300 further includes a gate insulator 160 sidewall providedalong the first sides 121 of the mesas 120 of the first plurality ofmesas 120. A gate conductor 150 sidewall is provided along the gateinsulator 160 sidewall. The gate conductor 150 may include graphene inone or more layers. According to the array 300 of vertical transistordevices 100 depicted in FIG. 11, a single gate insulator 160 sidewalland single gate conductor 150 sidewall are components of a single gate140 extending along the entirety of a column of mesas 120 of VFETdevices 100, on the first sides 121 of the mesas 120. Alternatively, aseries of separated gates 140 may extend along the first side 121 of themesas 120 of a column of mesas 120 of VFET devices 100.

The array 300 may further include, as depicted in FIG. 11, a second gateinsulator 160 sidewall provided along the second sides 122 of the mesas120 of the first plurality of semiconductor mesas 120. The array 300 mayfurther include a second gate conductor 150 sidewall provided along thesecond gate insulator 160 sidewall. The second gate conductor 150 mayinclude graphene in one or more layers. According to the array 300 ofvertical transistor devices 100 depicted in FIG. 11, a single gateinsulator 160 sidewall and single gate conductor 150 sidewall arecomponents of a single gate 140 extending along the entirety of a columnof mesas 120 of VFET devices 100, on the second sides 122 of the mesas120. Alternatively, a series of separated gated 140 may extend along thesecond side 122 of the mesas 120 of a column of mesas 120 of VFETdevices 100.

The mesas 120 within the VFET devices 100 of the array 300 may definechannel regions 130 (FIG. 1) passing between the first side 121 andsecond side 122 of the mesa 120. The channel region 130 may be incommunication with a source region (not shown) and drain region (notshown). The source and drain regions may be formed by any suitabletechnique known in the art.

The array 300 of vertical transistor devices 100 may further include oneor more additional pluralities of mesas 120 with the same array 300 asthe first plurality of mesas 120. The pluralities of mesas 120 may bespaced from one another, evenly and in parallel, by second trenches 210.

Each column of the array 300 has a width defined by the exteriorsurfaces of a pair of gate conductor 150 sidewalls, which width C may bethe width of each individual VFET device 100. Width C of each VFETdevice 100 is equal to or about equal to width M (FIG. 2) of the trenchseparating the originally-formed metal seeds 110. Therefore, the finalwidth C of the VFET device 100 may be scalable by adjusting the width Mof the formed metal seeds 110. In addition, the metal seeds 110 areformed at pitch, where “pitch” is known in the industry to refer to thedistance between identical points in neighboring features. Notably, thepitch of the metal seeds 110 is equal to or essentially equal to theresulting pitch of the formed VFET devices 100.

An array of vertical transistor devices is disclosed. The arraycomprises a first plurality of mesas extending above a substrate, afirst plurality of segments of insulator material, first gate insulatorsalong the first sides of the mesas of the first plurality of mesas, andfirst gate conductors along the first gate insulators, the first gateconductors comprising graphene. Each mesa of the first plurality ofmesas has a first side and a second side opposite the first side, thefirst sides aligned with one another, and the second sides aligned withone another. Each segment of insulator material separates one of themesas from another mesa within the first plurality of mesas.

A method for fabricating an array of vertical transistor devices is alsodisclosed. The method comprises forming a plurality of metal seeds upona substrate, forming a conductor material upon each of the plurality ofmetal seeds to form a plurality of gate conductors, forming a firstinsulator material upon each of the plurality of gate conductors to forma plurality of gate insulators, filling the first trench with a secondinsulator material, removing segments of the second insulator materialto expose underlying sections of the substrate and to define a pluralityof cavities, and filling the plurality of cavities with a channelmaterial to form channel regions bordered on a first side by the firstgate insulators and bordered on a second side by the second gateinsulators. A first gate insulator of the plurality of gate insulatorsis separated from a second gate insulator of the plurality of gateinsulators by a first trench.

It will be understood that the formed VFET device 100 and array 300 maybe thereafter subjected to additional processing to form top contacts,metal interconnects, additional stacked layers of VFET 100 arrays 300,and the like, the result of which may be the formation of a cross-pointmemory array. The additional processing may be conducted by conventionaltechniques, which are not described in detail herein.

With reference back to FIG. 10, also disclosed is an array of verticaltransistor devices 100, wherein the gate conductor 150 sidewalls arefurther provided along a vertical side of a metal seed line 110. Forexample, without limitation, the gate conductor 150 sidewalls of thearray 300 of VFET devices 100 may be provided along the first side 111and/or second side 112 of metal seeds 110.

FIGS. 12-21 depict various stages of processing a plurality of verticaltransistors in accordance with another embodiment of the present methodfor fabricating a semiconductor device, such as a VFET 100 device, aswell as for fabricating an array 300 of vertical transistor devices 100.FIGS. 12 and 13 depict identical stages of processing as those depictedin FIGS. 2 and 3, respectively. The description of FIG. 12 is equivalentto the description of FIG. 2, and the description of FIG. 13 isequivalent to the description of FIG. 3.

With reference to FIG. 14, the present embodiment of the method forforming a semiconductor device includes, following forming a conductormaterial upon the metal seeds 110 so as to form a gate conductor 150,forming an insulator material upon each of the plurality of gateconductor 150 sidewalls to faun a plurality of gate insulator 160sidewalls. The method of the present embodiment further includes formingthe insulator material upon a gate conductor 150 topwall or top side 116of the metal seeds 110. The insulator material may be formedconformally. Because the metal seeds 110 may be evenly spaced inparallel from one another, the formed gate insulator 160 sidewalls maybe evenly spaced from one another, such that each first trench 170,defined between opposing gate insulator 160 sidewalls, defines a width T(FIG. 14).

The method of the present embodiment includes leaving portions of thesubstrate 50 located within the first trenches 170 exposed. Leaving theportions of the substrate 50 within the first trenches 170 exposed maybe accomplished by forming the insulator material only upon the firstside 111, second side 112, and/or top side 116 of the metal seeds 110,but not upon the substrate 50 within the first trenches 170. Leaving theportions of the substrate 50 within the first trenches 170 exposed mayalternatively be accomplished by forming the insulator material upon thefirst side 111, second side 112, and top side 116 of the metal seeds 110and also upon the substrate 50 within the first trenches 170, followedby removal of the gate insulator 160 bottomwall (i.e., the insulatormaterial covering the substrate 50 within the first trenches 170). Theremoval of the insulator material may be accomplished by any suitabletechnique, including etching.

The insulator material of the gate insulator 160 sidewalls may be formedby any suitable technique, including, but not limited to, ALD,plasma-enhanced ALD, PVD, or other known methods. The insulator materialof the gate insulator 160 may comprise any suitable insulative material.For example, without limitation, the material of the gate insulator 160may be an oxide.

With reference to FIG. 15, the present embodiment of the method mayfurther include filling the first trench 170 with a second insulatormaterial 180. The second insulator material 180 may not only fill thefirst trenches 170, covering the exposed substrate 50, but may alsocover the gate insulator 160 top wall. Filling the first trenches 170with the second insulator material 180 may be accomplished by anysuitable method, including, without limitation, by spin coating, blanketcoating, CVD, PVD, in situ growth, or other known methods. The secondinsulator material 180 may be any suitable insulative material. Forexample, without limitation, the second insulator material 180 may be aconventional ILD material, such as silicon nitride.

With reference to FIG. 16, the present embodiment of the method mayfurther include, if necessary, removing portions of the second insulatormaterial 180, portions of the gate insulator 160 material, and portionsof the gate conductor 150 material, to expose the top sides 116 of themetal seeds 110. This may be accomplished by any suitable method,including, without limitation, abrasive planarization methods such aschemical mechanical polishing or planarization (“CMP”) or an etchingprocess.

With reference to FIGS. 17 through 19, the present embodiment of themethod may further include selectively removing segments of the secondinsulator material 180 to expose sections of the substrate 50 underlyingthe segments of second insulator material 180 removed. This may beaccomplished as described above with reference to FIGS. 7 through 9.

According to the present embodiment of the method, the bottom side 205of each cavity 200 is bordered by and defined by an exposed uppersurface of the substrate 50. The top side 206 of each cavity 200 remainsopen.

FIGS. 20 and 21 depict identical stages of processing as those depictedin FIGS. 10 and 11, respectively. The description of FIG. 20 isequivalent to the description of FIG. 10, and the description of FIG. 21is equivalent to the description of FIG. 11.

It will be understood that the formed VFET device 100 and array 300,depicted in FIG. 21, may be thereafter subjected to additionalprocessing to form top contacts, metal interconnects, additional stackedlayers of arrays 300 of VFET devices 100, and the like, the result ofwhich may be the formation of a cross-point memory array. The additionalprocessing may be conducted by conventional techniques, which are notdescribed in detail herein.

The VFET device 100 and array 300 may be used in a memory access device(not shown) that includes a memory cell (not shown) electrically coupledto the VFET device 100. The memory cell includes a top electrode (notshown) and a bottom electrode (not shown), which is coupled to a contact(not shown) for the drain. The source is coupled to another contact.Upon biasing of the source contact, the gate 140, and the top electrode,the VFET device 100 is turned “on” and current flows through the channelregion 130 and memory cell.

While the disclosed device structures and methods are susceptible tovarious modifications and alternative forms in implementation thereof,specific embodiments have been shown by way of example in the drawingsand have been described in detail herein. However, it should beunderstood that the present invention is not intended to be limited tothe particular forms disclosed. Rather, the present inventionencompasses all modifications, combinations, equivalents, variations,and alternatives falling within the scope of the present disclosure asdefined by the following appended claims and their legal equivalents.

1. A semiconductor device structure, comprising: a mesa extending abovea substrate, the mesa comprising: a channel region between a first sideand a second side of the mesa; a first gate on the first side of themesa, comprising: a first gate insulator; and a first gate conductorcomprising graphene overlying the first gate insulator.
 2. Thesemiconductor device of claim 1, further comprising: a second gate onthe second side of the mesa, comprising: a second gate insulator; and asecond gate conductor comprising graphene overlying the second gateinsulator.
 3. The semiconductor device of claim 2, further comprising:metal seeds on the first gate conductor, and metal seeds on the secondgate conductor.
 4. The semiconductor device of claim 2, wherein thesecond gate is operative to control, in conjunction with the first gate,current flow in the channel region.
 5. The semiconductor device of claim1, wherein the first gate conductor comprises at least one layer ofgraphene.
 6. The semiconductor device of claim 1, wherein a thickness ofthe first gate conductor is less than a thickness of the first gateinsulator.
 7. A method for fabricating a semiconductor device structure,comprising: forming a plurality of metal seeds upon a substrate; forminga conductor material upon each of the plurality of metal seeds to form aplurality of gate conductors; forming an insulator material upon each ofthe plurality of gate conductors to form a plurality of gate insulators,a first gate insulator of the plurality of gate insulators separatedfrom a second gate insulator of the plurality of gate insulators by afirst trench; and filling the first trench with a channel material toform a channel region.
 8. The method of claim 7, wherein forming aplurality of metal seeds comprises forming the plurality of metal seedssuch that the metal seeds are spaced from one another by a firstdistance and arranged in parallel.
 9. The method of claim 8, whereinforming the insulator material upon each of the plurality of gateconductors to form the plurality of gate insulators comprises formingthe insulator material such that the first trench has a width less thanthe first distance.
 10. The method of claim 7, wherein forming aconductor material upon each of the plurality of metal seeds comprisesforming at least one graphene layer upon each of the plurality of metalseeds.
 11. An array of vertical transistor devices comprising: a firstplurality of mesas extending above a substrate, each mesa of the firstplurality of mesas having a first side and a second side opposite thefirst side, the first sides aligned with one another, and the secondsides aligned with one another; a first plurality of segments ofinsulator material, each segment of insulator material separating one ofthe mesas from another mesa within the first plurality of mesas; firstgate insulators along the first sides of the mesas of the firstplurality of mesas; and first gate conductors along the first gateinsulators, the first gate conductors comprising graphene.
 12. The arrayof claim 11, further comprising: second gate insulators along the secondsides of the mesas of the first plurality of mesas; and second gateconductors along the second gate insulators, the second gate conductorscomprising graphene.
 13. The array of claim 11, wherein the first gateconductors are positioned along a vertical side of a metal seed.
 14. Thearray of claim 11, wherein each mesa comprises a channel region passingbetween the first side and the second side of the mesa.
 15. A method forfabricating an array of vertical transistor devices, comprising: forminga plurality of metal seeds upon a substrate; forming a conductormaterial upon each of the plurality of metal seeds to form a pluralityof gate conductors; forming a first insulator material upon each of theplurality of gate conductors to form a plurality of gate insulators, afirst gate insulator of the plurality of gate insulators separated froma second gate insulator of the plurality of gate insulators by a firsttrench; filling the first trench with a second insulator material;removing segments of the second insulator material to expose underlyingsections of the substrate and to define a plurality of cavities; andfilling the plurality of cavities with a channel material to formchannel regions bordered on a first side by the first gate insulatorsand bordered on a second side by the second gate insulators.
 16. Themethod of claim 15, wherein forming a conductor material upon each ofthe plurality of metal seeds comprises forming at least one graphenemonolayer upon each vertical side of the plurality of metal seeds. 17.The method of claim 15, wherein forming a first insulator material uponeach of the plurality of gate conductors comprises overlaying an oxidematerial upon each vertical side of the plurality of gate conductors.18. The method of claim 15, wherein filling the first trench with asecond insulator material comprises filling the first trench withsilicon oxide or silicon nitride.
 19. The method of claim 15, furthercomprising, after filling the plurality of cavities with the channelmaterial, removing the plurality of metal seeds.
 20. The method of claim15, wherein removing segments of the second insulator material comprisesselectively removing equally-spaced segments of the second insulatormaterial to expose equally-spaced sections of the underlying substrateand to define the plurality of cavities, and wherein the plurality ofcavities are equally-spaced.